This invention relates to a cable extension unit for displaying an image inputted through an image input source on an image outputting unit which is located away from the image input source through four signal lines, such as a LAN cable. More specifically, the invention relates to a cable extension unit for outputting sounds to an image output unit in addition to images.
Such kind of a conventional cable extension unit can output a RGB signal which is comprised of color signals (R signal, G signal, B signal) and synchronous signals (horizontal and vertical directions) as an image signal to be inputted from an image input source to an image output unit through four signal lines, such as a LAN cable belonging to Category 5. This unit can display an image inputted through an image input source on an image output unit which is located away therefrom without connecting the image input source and the image output unit with each other with a cable having a BNC (Bayonet Neill Concelman) connector or a DSUB connector, so that effective presentation can be realized, reducing the cost of the cable.
The image input source, such as a PC (personal computer), has a function of displaying a moving image with sounds. In order to realize more effective presentation, it is desirable that sound signals can be outputted to the image output unit together with a RGB signal with the above-mentioned cable extension unit.
The cable between the image input source and the image output unit in the above-mentioned cable extension unit is comprised of four signal lines, so the signal lines are needed to be further increased in order to output a sound signal together with a RGB signal to the image output unit. Then, the above-mentioned LAN cable can not be used, and the cost of the cable increases thereby.
Otherwise, in order to output a sound signal to the image output unit without increasing signal lines, a synchronous signal can overlap a color signal or a sound signal. But, it is difficult to recover the original synchronous signal since a synchronous signal has a polarity, so both signals are mixed with each other with only laying the synchronous signal on the color signal or the sound signal as it is.
Under this situation, the development of the cable extension unit with only four signal lines, such as a LAN cable, for outputting a sound signal to the image output unit together with a RGB signal has been desired.